Studying the repetitive extinction-ignition dynamics for lean premixed hydrogen-air combustion in a heated microchannel

The mechanism of repetitive extinction-ignition dynamics for lean premixed hydrogen–air mixture is studied in a microchannel with prescribed wall temperature. In this dynamics, the reacting flow is affected by the wall temperature and leads to ignition near walls. The flame expands in both downstream and upstream directions until flame bifurcation occurs. Part of the flame which propagates towards inflow consumes all the unburned mixture along its way. As the flame reaches cold inflow mixture, it extinguishes due to the heat loss. Another part of flame consumes the unburned mixture in downstream until the flame is extinguished. Afterward, unburned mixture fills the tube again until it is reignited. The repetitive extinction-ignition dynamics can be classified in five phases, namely, initiation phase, ignition phase, propagation phase, weak reaction phase, and flowing phase. Three peaks were detected for hydrogen–air mixture combustion which all appears in propagation and weak reaction phases. In the remaining phases two peaks were present. Details of flow field indicate that bifurcation of flame is due to creation of recirculation zones formed close to the walls at the beginning of ignition phase. The recirculation zones grow and merge, until a boundary zone is created in flow field with zero velocity.